1. Field of the Invention
The present invention relates to a fluid-communication mechanism for stably and effectively feeding liquid such as ink to, for example, a recording head or a pen as a liquid-using unit from an ink tank or the like serving as a liquid-storage and also for ejecting gas existing in the liquid-using unit to the liquid storage.
2. Description of the Related Art
Inkjet recording apparatuses form an image on a recording medium by accreting liquid ink onto the recording medium with a liquid-using unit, such as an inkjet recording head. These inkjet recording apparatuses have been used in recent years for performing a variety of printing job types, including color printing, since these apparatuses are relatively quite during recording and also allow small dots to be densely formed. One such inkjet recording apparatus includes an inkjet recording head receiving ink fed from an ink tank undetachably or detachably fixed to the apparatus; a carriage having the recording head mounted thereon so as to cause the recording head to relatively scan over a recording medium in a predetermined direction; and transporting means relatively transporting the recording medium in a direction perpendicular to the above-mentioned predetermined direction (that is, in a sub-scanning direction) and performs recording while discharging ink during the main scanning process of the recording head. Also, some of them have recording heads mounted on the carriage, discharging respective kinds of color ink, such as black, yellow, cyan, and magenta ink, so as to perform not only monochrome printing of a text image with black ink but also full color printing by changing the discharge ratio among these kinds of color ink.
In such an inkjet recording apparatus, gas, such as air entering an ink-feeding pathway or existing in the ink-feeding path, must be appropriately ejected.
Gas entering the ink-feeding pathway is generally classified into the following four types depending on where it comes from:    (1) gas entering from an ink-discharge port of a print head or generated in accordance with a discharging operation of the same;    (2) gas dissolved in ink;    (3) gas entering from outside through base material of which the ink-feeding pathway is composed, due to gas perminance; and    (4) gas entering when a cartridge-type ink tank is replaced with a new one.
Since a liquid path formed in an inkjet recording head has a very fine structure, ink fed from an ink tank to the recording head is required to be kept in a clean state in which no foreign particles such as dust is mixed. That is, when foreign particles such as dust are mixed, the foreign particles can clog in a discharge port, which is an especially narrow part of an ink flow path, or in a liquid flow path in direct communication with the discharge port, thereby sometimes preventing the recording head from performing a normal ink-discharging operation or from recovering its normal function.
In view of the above problem, many inkjet recording apparatuses generally have a filter member disposed in the ink flow path extending between the recording head and an ink-feeding needle protruding into the ink tank for preventing foreign particles from entering the recording head.
In recent years, in order to achieve high-speed recording, the number of discharge ports has increased, and a drive signal applied on an element generating energy for discharging ink has a higher frequency, thereby resulting in rapid increase in consumption of ink per unit time.
Although the above rapid increase causes an increase in ink passing through the filter member as a matter of course, in order to reduce a pressure loss caused by the filter member, it is effective to enlarge a part of the ink-feeding pathway so that the filter member disposed in the ink-feeding pathway has a large area. With this structure, when bubbles enter the ink-feeding pathway, they are likely to remain upstream of the filter member in the enlarged part of the ink-feeding pathway and are unlikely to be ejected, thereby preventing ink from being smoothly fed. Also, there is a risk that a fine bubble formed from gas remaining in the ink-feeding pathway is mixed in ink being introduced to the discharge port and inhibits the ink from being discharged.
Accordingly, it is important that gas remaining in the ink-feeding pathway be smoothly removed, and some methods for solving the above problem are proposed.
One such proposal is a cleaning operation described below.
Since an inkjet recording head performs printing by discharging liquid ink, for example, in a form of a droplet from its discharge port disposed facing a recording medium, the discharge port is sometimes clogged with ink having an increased viscosity, solidified ink due to its evaporation from the discharge port, dust accreted on the discharge port, bubbles entering the liquid path including the corresponding discharge port, or the like, thereby resulting in poor-quality of printing.
As a countermeasure against the above problem, the inkjet recording apparatus has a capping member disposed therein for covering the discharge port of the recording head when the head is in a non-printing operation mode, or a wiping member disposed therein for wiping the surface (discharge-port-forming surface) of the recording head if necessary. The capping member serves as a cap for preventing ink in the discharge port from the above-mentioned dehydration in a printing operation halt mode. Also, when the discharge port is clogged, the capping member covers the discharge-port-forming surface and to solve clogging of the discharge port due to solidification of ink in the discharge port, due to insufficient discharge of ink in the liquid flow path due to its increased viscosity, and due to insufficient discharge of ink due to bubbles mixed in the ink by exerting a negative pressure on the discharge port, generated by, for example, a suction pump in communication with the inside of the capping member so as to suck ink in the discharge port and to eject it from the discharge port.
A process forcefully ejecting ink for solving these problems of insufficient discharge is called a cleaning operation. This cleaning operation is executed, for example, when a print operation is restarted after long halt of the apparatus or when an operator detects deterioration in quality of recording image and operates, for example, a cleaning switch. In addition, a wiping operation is performed by the wiping member having an elastic plate composed of rubber or the like after ink is forcefully ejected as described above.
Also, during an initial filling period for filling ink in the flow path or liquid path of the recording head for the first time, or during the cleaning operation performed when the ink tank is replaced with a new one, bubbles remaining in the ink-feeding pathway are ejected at a high flow speed achieved by exerting a large negative pressure on the capped discharge-port-forming surface by driving the suction pump at high speeds.
Unfortunately, when the area of the filter member is increased so as to inhibit a dynamic pressure of the foregoing filter member, the area of the flow path is also increased. Hence, even when a large negative pressure is generated in the flow path by the foregoing cleaning operation, a high flow speed at which bubbles are effectively transferred is not achieved, whereby it is very difficult to remove bubbles staying in the ink-feeding pathway from the discharge port by the suction pump. In other words, as a condition under which bubbles pass through the filter member with the flow of ink generated by the suction pump, although ink is required to pass through the filter member at a predetermined flow speed or higher, a large difference in pressures between the both sides of the filter member must be generated in order to achieve such a flow speed. In order to achieve such a condition, in general, a flow-path resistance is increased by making the area of the filter member smaller or a suction pump having a larger capacity is used. In the former case, making the filter member smaller causes deterioration in performance of feeding ink to the head. In the latter case, even when removal of gas is tried with a large amount of flowing ink, a large amount of ink is ejected, thereby sometimes ending up consuming an amount of ink more than necessary.
With the above situation in mind, there are two other methods of removing bubbles: (1) ejecting bubbles directly outside; and (2) moving it to an ink tank and trap it in a part of the ink tank, which does not prevent ink from being fed. Although the former requires a structure in which a communication port extending to the outside is disposed in the feeding path, such a method is not preferable because of the following reason.
In many normal inkjet recording apparatuses, in order to prevent ink from leaking accidentally from the discharge port, a capillary-force-generating member such as a form is disposed in the ink tank or a negative pressure is generated in an ink-storing space in the ink tank by disposing an elastic member such as a spring, in a flexible ink-storing bag so as to exert an urging force on the bag and thus to increase the internal volume of the bag. In such a case, when the communication port merely for removing bubbles is disposed in the feeding path, atmospheric air enters the feeding path contrarily from the communication port, resulting in releasing the negative pressure. In order to avoid this problem, a pressure-regulating valve or the like must be disposed in the communication port, thus leading to complicated and increased structures of the ink-feeding system and the recording apparatus including the ink-feeding system. Also, in order to prevent ink from leaking from a bubble-ejection communication port, since a water-repellent film or the like allowing gas to pass therethrough and preventing liquid from passing therethrough must be disposed in the port, or since a device (a mechanism detecting an amount of bubbles, opening or closing the communication port, or the like) is needed, which opens the communication port and ejects bubbles through the port only when bubbles remain in the ink-feeding pathway, thereby resulting in an increased manufacturing cost or a complicated structure having an increased size.
The method of moving bubbles to the ink tank will be discussed. In this case, if ink in the ink tank, having an amount corresponding to the volume of bubbles to be moved to the ink tank can be transferred to the head, this method is preferable because a negative pressure equivalent to a holding force of a meniscus formed in the discharge port can be exerted on the recording head while the internal volume of the ink tank does not fluctuate, and the generated negative pressure is kept constant. Also, if bubbles can be moved to the ink tank, and when the ink tank is of a cartridge type, since it is replaced with a new one upon having no ink stored therein and accordingly the bubbles can be completely removed from the ink-feeding line, this structure is preferable.
However, many inkjet recording apparatuses widely available in the market as consumer-oriented products have a structure in which cartridge-type ink tanks having black ink and respective kinds of color ink stored therein are detachably placed on the recording head or the carriage having the recording head mounted thereon from above. That is, many ink cartridges feed ink to the recording head by having, for example, a hollow ink-feeding needle protruding therein, mounted upward on the carriage. Accordingly, the inside tube diameter of the ink-feeding needle connecting the ink cartridge and the recording head to each other is a matter of discussion. That is, although, the feeding needle is required to be thin for easily placing the cartridge with a small force, the smaller the internal tube diameter, a meniscus force becomes greater accordingly, whereby bubbles are unlikely to move smoothly.
Meanwhile, some mechanisms for moving bubbles to the ink tank are proposed.
For example, Japanese Patent Laid-Open No. 5-96744 discloses a structure in which the recording head is separated into a first compartment including an atmosphere communication port and a second compartment including a capillary-force-generating member, the first compartment and the ink tank are connected by at least two communication paths having openings in the first compartment, whose heights are different from each other, and air is fed to the ink tank through one of the communication paths. With such a structure, a negative pressure is exerted on the recording head with the head between the first compartment and the second compartment or by the capillary-force-generating member disposed in the second compartment, and the first compartment has the atmosphere communication port disposed therein.
Unfortunately, the structure disclosed in Japanese Patent Patent Laid-Open No. 5-96744 is intended to introduce air into an undeformable ink tank in accordance with ink-feeding so as to use up ink in the ink tank, and is not intended to eject bubbles remaining in the ink-feeding pathway to the ink tank. That is, the art disclosed in the above patent document is not applicable for transferring gas in the ink-feeding pathway, in particular, in the second compartment or in the recording head, to the ink tank.
As another proposal, U.S. Pat. No. 6,460,984 discloses a structure in which, when a chamber for storing a negative-pressure-generating member and a liquid-storing chamber are disposed so as to be separable from each other, a gas priority vent path and a drain path are disposed in a connecting portion connecting these chambers so as to reliably introduce gas to the liquid-storing chamber. However, in the structure disclosed in this patent document, the ink tank and the recording head likewise have a capillary-force-generating member and an atmosphere communication port disposed therebetween, and gas can enter or come out freely through an opening of an ink-feeding path as the atmosphere communication port. Hence, similar to Japanese Patent Patent Laid-Open No. 5-96744, the ink-feeding path is open to the atmosphere; accordingly, the art disclosed in this patent document is not applicable for ejecting bubbles remaining in the ink-feeding pathway.
In addition, U.S. Pat. No. 6,347,863 discloses an ink container (50) having a structure in which drain conduits (66, 72, 74) and vent conduits (76, 82, 84) protrude downward, each drain conduit has an upper opening in the bottom of the inner wall, and each vent conduit has an opening disposed in the ink storing space of the container. An object of the art disclosed in the above patent document is intended to make up a system for refilling a member (14) including reservoirs (16, 18, 20) with ink, and is not intended to remove bubbles remaining in the ink-feeding pathway downstream of the reservoirs or in an ink-using unit. Also, since the heights of lower openings of the drain conduit and the vent conduit are not equal to each other, a meniscus once formed in either conduit may prevent liquid or gas from moving. Although no description about the atmosphere communication port is found in the above patent document, when a system made up by the ink container 50 and the member 14 has an enclosed structure, since continuous use of ink causes the inner negative pressure of the system to increase rapidly and hence makes it impossible to feed ink to the ink-using unit, it is imagined that an atmosphere communication port is disposed in any one of components. In view of the structure of each of the reservoirs (16, 18, 20) having a form (90) stored therein and the structures and the functions of the ink container, the vent conduits, and so forth shown in FIG. 2 in the patent document, it is imagined that each of the reservoirs (16, 18, 20) has an atmosphere communication port disposed therein. In either case, the art disclosed in the document has no intention to positively eject bubbles generated from any of the gas generally classified into the above-described (1) through (4) and remaining in the ink-feeding pathway.
Further, U.S. Pat. No. 6,022,102 discloses a structure in which, a refilling tank for refilling a reservoir tank including a chamber for storing a negative-pressure-generating member and an ink-storing chamber with ink can be connected to the reservoir tank, and when the refilling tank is connected to the same in the upper and lower parts of the space of the ink-storing chamber, while ink is introduced from the refilling tank to the ink-storing chamber through a liquid communication conduit lying in the lower part, air is introduced from the ink-storing chamber to the refilling tank through a gas communication conduit lying in the upper part. However, the structure disclosed in the above patent document, in which the ink-storing chamber and the recording head likewise have a negative-pressure-generating member and an atmosphere communication port disposed therebetween, essentially makes no difference from those disclosed in Japanese Patent Patent Laid-Open No. 5-96744 and U.S. Pat. No. 6,460,984; accordingly, the art disclosed in the above-document is inapplicable for ejecting bubbles remaining in the ink-feeding pathway.
Also, as shown in FIG. 20, U.S. Pat. No. 6,520,630 discloses the structure of an ink-feeding system in which a sub-tank 1022 for refilling a main tank 1020 in communication with a recording head 1018 with ink is placed on the top of the main tank, in accordance with acceleration or deceleration of a carriage, while gas in the main tank is introduced to the sub-tank, ink in the sub-tank is fed to the main tank. In the structure disclosed in the above-document, although ink is stored in the main tank in communication with the sub-tank in a free state, the main tank includes means for introducing atmospheric air into the main tank, whereby the structure essentially makes no difference from those disclosed in Japanese Unexamined Patent Application Publication No. 5-96744, and U.S. Pat. Nos. 6,460,984 and 6,022,102. In other words, the art disclosed in the above document has no intention to positively eject bubbles generated from any of the gas generally classified into the above-described (1) through (4) and remaining in the ink-feeding pathway.
Common structures disclosed in Japanese Patent Laid-Open No. 5-96744, U.S. Pat. Nos. 6,460,984, 6,022,102, and 6,520,630 are a detachable liquid storage (ink tank) in communication with the recording head through a plurality of communication paths, and atmospheric air-introducing means provided downstream of the communication paths (close to the recording head). Problems of the common structures will be described below with reference to U.S. Pat. No. 6,520,630.
FIG. 20 is a conceptual view illustrating the structure of an ink-feeding system disclosed in U.S. Pat. No. 6,520,630. Assuming that air movement (air movement to a sub-ink chamber 1081 of the sub-tank 1022 through a pipe 1056A) is at a halt in a state illustrated in the figure, the balance among forces exerted on a meniscus formed in the pipe 1056A will be discussed. Downward forces consists of a pressure Ha generated due to the head between the ink level in the sub-ink chamber 1081 and the position of a meniscus formed in the pipe 1056A and a meniscus force MA. Also, an upward force is a pressure P generated due to air stored in an ink bag 1100 disposed in the main tank 1020. With all these forces being balanced, the air movement is at a halt. In this case, the air pressure P balances with the sum of the pressure HA generated due to the head between the ink level in the sub-ink chamber 1081 and the meniscus position in the pipe 1056A (P=HA+MA). In addition, since ink in the sub-ink chamber 1081 and that in the ink bag 1100 are in communication with each other through a pipe 1056B, a difference in a downward ink pressure exerted on the meniscus formed in the pipe 1056A and the air pressure in the ink bag 1100 is equal to a pressure HB−HA generated due to the head between the meniscus position in the pipe 1056A and the ink level in the ink bag 1100. Resultantly, the pressure HB−HA generated due to the above head balances with the meniscus pressure MA, thereby keeping the equivalent state.
When ink is further consumed in this state, and the ink level in the ink bag 1100 is lowered because of, for example, introduction of bubbles from a bubble-generating device 1104, the pressure HB−HA generated due to the head between the meniscus position in the pipe 1056A and the ink level in the ink bag 1100 increases, and when it finally exceeds the meniscus pressure, air is introduced to the sub-ink chamber 1081, whereby ink in the sub-ink chamber 1081 is fed to the ink bag 1100.
However, when ink is discharged by the recording head 1018, since ink flows through the entire feeding system, a pressure loss occurs between the sub-ink chamber 1081 and the ink bag 1100 in accordance with a flow rate in the pipe 1056B. Accordingly, in addition to the foregoing meniscus pressure MA and the pressure HB−HA generated due to the head between the meniscus position and the ink level in the ink bag 1100, the pressure loss must be taken into account. As a result, the air movement occurs when the pressure generated due to the head between meniscus position and the ink level in the ink bag 1100 is greater than the sum of the foregoing meniscus pressure and the pressure loss. In other words, in comparison to the air-movement halting state, in an ink-discharging state or dynamic state, exchange between gas and liquid (hereinafter, simply referred to as gas-liquid exchange) does not take place only after the ink level in the ink bag 1100 is further lowered by an amount corresponding to the pressure loss in the pipe 1056B in accordance with the flow rate in the same. When the ink level at which the gas-liquid exchange starts to take place is lowered than the opening of the pipe 1056B, the gas-liquid exchange does not take place, whereby ink in the main tank 1020 is used up while ink in the sub-tank 1022 remains unused.
Accordingly, when the pipe is made thinner in order to easily place the ink tank as described above, since the pressure loss increases accordingly, the fact that the liquid level in the main tank at which the gas-liquid exchange starts to take place is lowered in accordance with an increase in the pressure loss must be taken into account. In other words, the size of the main tank inevitably increases, thereby leading to an increased size of the entire recording apparatus.
In addition, the structure shown in FIG. 20 has another problem in that the bubble-generating device 1104 is disposed in the lower part of the main tank. That is, in spite of a strong request about a structure in which transfer of bubbles to the discharge port of ink can be minimized, there is a risk that, in accordance with an ink discharge operation of the recording head, bubbles introduced from the bubble-generating device 1104 are drawn into a flow path 1041 in communication with the recording head 1018, together with ink flowing toward the recording head 1018. Accordingly, in order to prevent such bubbles from being drawn, it is necessary to restrict flow of ink in accordance with the ink discharge operation or to dispose the bubble-generating device 1104 remote from a filter member 1039, and any of these measures causes a further increased size of the main tank 1020.
The structures disclosed in Japanese Patent Laid-Open No. 5-96744, U.S. Pat. Nos. 6,460,984 and 6,022,102, in which the atmospheric air-introducing means is provided downstream of the communication paths, close to the recording head have the same disadvantages as described above.
As described above, although the foregoing Japanese Patent Laid-Open No. 5-96744, U.S. Pat. Nos. 6,460,984, 6,347,863, 6,022,102, and 6,520,630 disclose the art that gas is introduced to the ink tank lying uppermost-stream, but according to these patent documents, any of the purposes that, in an operating state of the apparatus, gas remaining in the ink-feeding pathway having an enclosed structure, that is, the gas generally classified into the foregoing kinds (1) through (4), entering the ink-feeding pathway and staying there is smoothly transferred to the ink tank and that the gas is trapped in the same has not been achieved. In addition, according to the foregoing patent documents, when a flow rate of ink is increased so as to perform high-speed recording, sometimes, the apparatus fails to follow the flow rate for feeding ink and runs out of ink, or bubbles enter the recording head. In order to prevent the above problems, the size of the recording head is inevitably increased.